OK, so I've scoured various threads and other sites and can't find a clear answer to another (rather obvious) question from a credible source. If you have a big old canister filter, why not feed the co2 into the inbound hose? Wouldn't the impeller and all the travel through the hoses and media etc. mix it up nicely with the water so when it comes out into the tank it is dispersed? I'm guessing one possible answer is that the co2 level in the filter might muck with the bacteria. Maybe there is something even more obvious. I read something about voiding warranties but that doesn't really pass the "so what?" test... Thanks for any answers!

OK, so I've scoured various threads and other sites and can't find a clear answer to another (rather obvious) question from a credible source. If you have a big old canister filter, why not feed the co2 into the inbound hose? Wouldn't the impeller and all the travel through the hoses and media etc. mix it up nicely with the water so when it comes out into the tank it is dispersed? I'm guessing one possible answer is that the co2 level in the filter might muck with the bacteria. Maybe there is something even more obvious. I read something about voiding warranties but that doesn't really pass the "so what?" test... Thanks for any answers!

Most people have or, will try it at some point. It will work as you would expect but, the CO2 will also accumulate into large bubbles inside the filter and then belch out the bubbles every once in awhile. It becomes annoying to see and makes you think you are wasting CO2. Maybe not the best solution but, will work until you put together a better solution.

Your intuition is correct. The thought is that the inbound CO2 acdifies the water and creates a less than an ideal environment for the bacteria. There is also the reality that the CO2 won't dissolve entirely and will create pockets in the filter, making noise and other problems, especially if your pump is in the top of the canister. There are plenty of people who do inject right into the canister and I'm sure have good results. I know I used to, and although the accumulated CO2 was an annoyance, beyond that I can't think of anyone or any "study" that concluded that it was a bad thing. Trouble with my setup is that I run an FX5 which moves about 5 gallons per minute real world, and not a lot of CO2 was getting dissolved before either making a bubble on the underside of the lid, or getting blasted into the tank due to pressure (both actually - the bubble would get big enough and the filter would shotgun it into the tank rather dramatically). That also meant that to get to desired levels of CO2 in the water, I wasted a lot of it. With the Cerges, I halved my bubble count and get better solution.

I have never heard of a warranty being denied for CO2 injection. I suppose it could happen but I would be really interested in hearing the manufacturer explain why

sjb1987: 500 gph "real flow" would probably be way too much. I have a Mag 5 which is in that range and I have to throttle it back with a ball valve on the output side, even with the scrubbies in there. Trouble is that manufacturers LIE about their true flow rates so trying to figure out what will or won't work is daunting. I would go for more than you think you need and then design in a way to restrict flow to a useable rate either with a gate or ball valve of some kind. Also think about removing/cleaning these things a bit ahead of time. Priming them is a pain so putting valves/unions on the piping is going to make R and R a lot easier.

thanks for the response moose.... i have a cerges reactor on my 75 gal with a 750gph pump but i "y"ed off the pump so it probably only has about 300gph goin through it... im setting up a new 40b and will be using the cfs500 from aquatraders.com and they are rated for 500gph and push every bit of it too..i did not want to "y" off this setup due to lack of space.. ill do some playin around with my 75 and see if i can get close to around 500gph on the reactor side
thanks

Thank you for the responses. I'm thinking of a 70 gallon and will probably put an FX7 or comparable on it. Clearly, I need to avoid running the co2 into the filter. BTW, you are correct regarding the fabricated throughput numbers: I recently saw this referenced in the small print in a mfg's literature -- they said the throughput was measured without any media or trays in the filter and with no tubing. Nice touch! The only good news is they probably all do it so you have an apples to apples situation when comparing filters. Thank you all again.

I don't know if you've checked out some of the mods people do to the CFS500, but they're pretty interesting. I have one as a backup. Used it for about a year before I upgraded to the FX5 which is like it's big brother. The CFS500 doesn't have any media baskets in it so modding it made sense. Check out the thread(s) by CWO4GUNNER here and on APC. Informative. Be aware that they've updated their lids and improved the filter as time went on so that the problems people were complaining about early in these threads were more or less all addressed. I bought mine off of TopDogSellers on e-bay. They were quick to make me happy when I had issues (I broke the down-tube on my first one - not the filter's fault. I was being a derpy derp).

I tried adding the 2 scrubbers and it didn't really help. The small microbubbles get sucked right through.

Even when I turn the flow down low enough that the large bubbles only make it a few inches down the housing, the microbubbles still make it all the way to the bottom. I'm surprised I'm having this problem with the 20" housing. I must have been getting down to 200gph or so.

Any other suggestions? I'm about to give up and use a separate small pump to drive the reactor, which is disappointing since I would never have built a 20" Cerges if I knew was going to have to run a separate pump for it anyway.

I'm not sure how to answer you. The point of a CO2 reactor is to get CO2 into the water. It's not a filter. GPH shouldn't even be factored here, within reason. If it takes 80 or 100 GPH or less and dissolves the desired amount of CO2 into the water, what's the problem? Circulating that water is the job of the main filter, and whatever else you have in the tank to facilitate movement.

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